1. Field of the Invention
The present invention relates to a polypropylene resin composition containing two kinds of specified propylene-ethylene block copolymers having mutually different structures. More particularly, it relates to a polypropylene resin composition providing a molded article excellent in appearance when formed into a molded article because few flow marks are generated. For example, the die swell is high and few fish eyes are generated. Further, the present invention relates to a molded article made of the polypropylene resin composition.
2. Description of Related Arts
Polypropylene resin compositions are materials excellent in rigidity, impact resistance, and the like and they have been used widely as molded articles such as automobile internal and external trim materials, electrical parts housings, and the like. It is well known that, among these polypropylene resin compositions, a polypropylene resin composition containing propylene-ethylene block copolymers, for example, a polypropylene resin composition containing a propylene-ethylene block copolymer and a propylene homopolymer, or different two kinds of propylene-ethylene block copolymers is preferably used because of its excellent rigidity, impact resistance, and the like.
For example, JP 07-157626A discloses a thermoplastic resin composition containing a propylene-ethylene block copolymer obtained by multi-stage polymerization and a polyolefin rubber. The propylene-ethylene block copolymer is composed of a propylene-ethylene block copolymer in which the ethylene content of a propylene-ethylene random copolymer phase is from 5 to 50% by weight and the intrinsic viscosity of the copolymer phase is from 4.0 to 8.0 dl/g, and a propylene-ethylene block copolymer in which the ethylene content of a propylene-ethylene random copolymer phase is more than 50% by weight to 98% by weight and an intrinsic viscosity of the copolymer phase is 2.0 to less than 4.0 dl/g. Further, it is disclosed that the thermoplastic resin composition having an extremely large ductility can be obtained.
JP 07-157627A discloses a thermoplastic resin composition containing a propylene-ethylene block copolymer obtained by multistage polymerization and a polyolefin rubber. The propylene-ethylene block copolymer is composed of a propylene-ethylene block copolymer in which the intrinsic viscosity of a propylene-ethylene random copolymer phase is from 4.0 to 8.0 dl/g, and a propylene-ethylene block copolymer in which the intrinsic viscosity of a propylene-ethylene random copolymer phase is 2.0 to less than 4.0 dl/g excluding the propylene-ethylene block copolymer of JP 07-157626A. Further, it also discloses that the thermoplastic resin composition having a extremely large ductility can be obtained.
Moreover, JP 07-233305A discloses a polypropylene resin composition improved in flowability, containing a polypropylene, an inorganic filler, and a metallic soap composed of a fatty acid of 15 to 20 carbon atoms and zinc, and having an improved flowability. As the polypropylene, a block copolymer containing a propylene-ethylene copolymer portion having an [xcex7] of 2 to 6 dl/g and having an [xcex7] of 7 to 15 dl/g is disclosed. As the preferred embodiment, it discloses the composition composed of at least two kinds of block copolymers. And, it discloses that there can be obtained a polypropylene resin composition having, in practical use, no problem of reduction of impact strength, rigidity, heat resistance, and the like, and being suitable for manufacturing a thin-walled molded article because of its improved flowability.
Incidentally, in recent years, a propylene-ethylene block copolymer, which is preferably used because of its excellent rigidity, impact resistance, and the like, has become manufactured by a continuous gas phase process whereby the manufacturing step is simple, and manufacturing can be performed at a low cost. However, in general, the propylene-ethylene block copolymer manufactured by the gas phase process has the following problems. If the intrinsic viscosity of the propylene-ethylene random copolymer portion is set high, granular structures generate, whereby the appearance of the molded article becomes poor.
As a method for solving such a problem of the appearance, for example, JP 07-286075A discloses a propylene polymer composition which comprises a propylene polymer manufactured by a continuous polymerization method, wherein the propylene polymer has a content of a 23xc2x0 C. n-decane soluble component of from 0 to less than 15% by weight. The 23xc2x0 C. n-decane soluble component contains a structural unit derived from ethylene in an amount of from 30 to 60 mol % and has an intrinsic viscosity [xcex7] of from 3 to 7.5 dl/g, and a propylene block copolymer produced by a batch-wise or continuous solvent polymerization method, wherein the propylene block copolymer has a content of a 23xc2x0 C. n-decane soluble component of from 15 to 40% by weight. The 23xc2x0 C. n-decane soluble component contains a structural unit derived from ethylene in an amount of from 30 to 60 mol % and has an intrinsic viscosity [xcex7] of from 5 to 12 dl/g. It also discloses that the propylene polymer composition is obtainable that is excellent in rigidity and impact resistance, and is capable of being formed into a molded article without generating granular structures on its surface.
However, it has been desired to develop a polypropylene resin composition without generating flow marks on its surface when formed into a molded article. In other words, it is desired to improve appearance, and ensure practical use even when granular structures are generated.
An object of the present invention is to provide a polypropylene resin composition providing a molded article excellent in appearance when formed into a molded article, i.e., having few flow marks. In other words, die swell is high and few fish eyes are generated.
Further, another object of the present invention is to provide a molded article made of a polypropylene resin composition.
In view of the present situation, the present inventors as a result of intensive study, have found that a polypropylene resin composition obtained by using two kinds of specific propylene-ethylene block copolymers which are mutually different in structure, can solve the foregoing problems. Thus, they have completed the present invention.
Namely, the present invention relates to a polypropylene resin composition comprising:
(A) 95 to 80% by weight of a polypropylene resin selected from the group consisting of a propylene-ethylene block copolymer (i) having a propylene homopolymer portion and propylene-ethylene random copolymer portion, and (ii) a mixture of the propylene-ethylene block copolymer (i) and a propylene homopolymer, wherein an intrinsic viscosity [xcex7]AP of the propylene homopolymer portion when the resin (A) is the copolymer (i), or of the total of the propylene homopolymer portion and the propylene homopolymer when the resin (A) is the mixture (ii) is not more than 1.3 dl/g, and an intrinsic viscosity [xcex7]AEP of the propylene-ethylene random copolymer portion is not more than 3.0 dl/g; and
(B) 5 to 20% by weight of a propylene-ethylene block copolymer composed of a propylene homopolymer portion and propylene-ethylene random copolymer portion wherein an intrinsic viscosity [xcex7]BEP of the propylene-ethylene random copolymer is 8.0 to 15 dl/g, and wherein the polypropylene resin composition has a melt flow rate (MFR) of from 5.0 to 150 g/10 min., and the sum of the (A) and (B) is 100% by weight.
Below, the present invention will be described in detail.
The propylene-ethylene block copolymer (i) used in the present invention is a propylene-ethylene block copolymer having a propylene homopolymer portion (hereinafter, sometimes referred to as xe2x80x9cfirst segment of the copolymer (i)xe2x80x9d), and a propylene-ethylene random copolymer portion (hereinafter, sometimes referred to as xe2x80x9csecond segment of the copolymer (i)xe2x80x9d). Further, two or more kinds of propylene-ethylene block copolymers satisfying the above-conditions of the copolymer (i) may also be used.
The mixture (ii) is a mixture of the propylene-ethylene block copolymer (i) and a propylene homopolymer. Further, the mixture may be formed by using two or more kinds of propylene-ethylene block copolymers and two or more kinds of propylene homopolymers.
The polypropylene resin (A) used in the present invention is selected from the propylene-ethylene block copolymer (i) having a propylene homopolymer portion and a propylene-ethylene random copolymer portion, or a mixture (ii) of the propylene-ethylene block copolymer (i) and a propylene homopolymer. Herein, the propylene homopolymer portion of the polypropylene resin (A) denotes the propylene homopolymer portion which is the first segment of the propylene-ethylene block copolymer (i) when the resin (A) is the block copolymer (i), and the total of the propylene homopolymer portion which is the first segment of the propylene-ethylene block copolymer (i) and the propylene homopolymer when the resin (A) is the mixture (ii).
The intrinsic viscosity of [xcex7]AP of the propylene homopolymer portion of the polypropylene resin (A) is not more than 1.3 1/g, and preferably from 0.7 to 1.3 dl/g. If the [xcex7]AP exceeds 1.3 d/l, the melt flow rate (MFR) of the polypropylene resin composition may be reduced, depending on the composition and conditions resulting in a reduction in flowability.
Herein, when the resin (A) is the mixture (ii) of the copolymer (i) and the propylene homopolymer, the intrinsic viscosity of [xcex7]AP refers to the viscosity of a mixture of the propylene homopolymer portion of the copolymer (i) and the propylene homopolymer. It is possible to determine the intrinsic viscosity [xcex7]AP of the propylene homopolymer portion by using the intrinsic viscosity of the propylene homopolymer portion which is the first segment of the propylene-ethylene block copolymer (i), the intrinsic viscosity of the propylene homopolymer, and the mixing ratio thereof because the additive property holds for the intrinsic viscosity in the mixture.
The isotactic pentad fraction of the propylene homopolymer portion of the copolymer (i) and the propylene copolymer in the polypropylene resin (A), determined by 13C-NMR is preferably not less than 0.95, and more preferably not less than 0.97 from the viewpoints of rigidity, heat resistance, and the like.
The intrinsic viscosity [xcex7]AEP of the propylene-ethylene random copolymer portion of the copolymer (i) is not more than 3.0 dl/gl, and preferably from 1.5 to 3.0 dl/g. If the intrinsic viscosity [xcex7]AEP exceeds 3.0 dl/g, a large number of granular structures may be generated in the molded product.
The aforementioned granular structure is an agglomerate product mainly composed of a propylene-ethylene random copolymer component occurring due to the low dispersibility of the propylene-ethylene random copolymer portion of the polypropylene resin (A), and it has a size of from about 100 to several hundred micrometers. When a molded product is formed with injection molding, or the like, by using a material in which a large number of granular structures are present, not only is the appearance of the molded product surface damaged, but also the mechanical properties such as the impact resistance performance are adversely affected.
Further, the ethylene content [(C2xe2x80x2)EP] of the propylene-ethylene random copolymer portion in the polypropylene resin (A) is preferably from 20 to 60% by weight, and more preferably from 25 to 55% by weight from the viewpoint of the impact resistance.
From the viewpoints of impact resistance, rigidity, heat resistance, and the like, the respective proportions of the propylene-ethylene random copolymer portion of the polypropylene resin (A) and the propylene homopolymer portion of the polypropylene resin (A) are as follows: preferably, the proportion of the propylene-ethylene random copolymer portion of the polypropylene resin (A) is 5 to 30% by weight, more preferably 7 to 20% by weight, and the proportion of the propylene homopolymer portion in the copolymer (i) when the resin (A) is the copolymer (i), or of the total of the homopolymer portion of the copolymer (i) and the propylene homopolymer when the polypropylene resin (A) is the mixture(ii), is from 95 to 70% by weight, more preferably 93 to 80% by weight. The sum of the propylene homopolymer portion(i) or of the total of the homopolymer portion of the copolymer (i) and the propylene homopolymer, and the propylene-ethylene random copolymer portion is 100% by weight.
The manufacturing method of the propylene-ethylene block copolymer (i) and propylene homopolymer in the propylene resin (A) used in the present invention has no particular restriction. However, the invention can be preferably produced by a known polymerization method with a catalyst system formed from (a) a solid catalyst component containing magnesium, titanium, halogen and an electron donor as essential components, (b) an organoaluminum compound, and (c) an electron donor component, for example, a catalyst system described in U.S. Pat. Nos. 4,983,561, 5,608,018, or 6,187,883, or the like, adjusting polymerization conditions so that the resin can be produced.
From the industrial and economical viewpoints (viewpoint of simplicity of the steps), the polymerization form is preferably a continuous gas phase polymerization.
The propylene-ethylene block copolymer (B) used in the present invention is a propylene-ethylene block copolymer composed of a propylene homopolymer portion (hereinafter, referred to as xe2x80x9cfirst segment of the copolymer (B)xe2x80x9d) and a propylene-ethylene random copolymer portion (hereinafter, referred to as xe2x80x9csecond segment of the copolymer (B)xe2x80x9d).
The intrinsic viscosity [xcex7]BP of the propylene homopolymer portion which is the first segment of the copolymer (B) is preferably not more than 1.3 dl/g, and more preferably not more than 1.1 dl/g from the viewpoints of the flowability of the polypropylene resin composition.
The isotactic pentad fraction of the propylene homopolymer portion which is the first segment of the copolymer (B), determined by 13C-NMR is preferably not less than 0.95, and more preferably not less than 0.97 from the viewpoints of rigidity, heat resistance, and the like.
The intrinsic viscosity [xcex7]BEP of the propylene-ethylene random copolymer portion which is the second segment of the copolymer (B) is from 8.0 to 15 dl/g, and preferably from 9.0 to 13 dl/g. If the [xcex7]BEP is less than 8.0 dl/g, the die swell may be insufficient, so that the flow marks may generate. Whereas if it exceeds 15.0 dl/g, a large number of granular structures may occur, or the MFR of the polypropylene resin composition may be reduced, resulting in a reduced flowability.
The aforementioned granular structure is the same one as the granular structure in the polypropylene resin (A).
The ethylene content [(C2xe2x80x2)EP] of the propylene-ethylene random copolymer which is the second segment of the copolymer (B) is preferably from 20 to 60% by weight from the viewpoint of impact resistance.
From the viewpoints of impact resistance, die swell, and flow mark of the molded article, and the MFR and flowability of the polyolefin resin composition, the respective proportions of the propylene-ethylene random copolymer portion which is the second segment of the copolymer (B), and the propylene homopolymer portion which is the first segment of the copolymer (B) are as follows: the proportion of the second segment of the copolymer (B) is preferably from 10 to 40% by weight, and preferably 15 to 35% by weight, and the proportion of the first segment of the copolymer (B) is preferably from 90 to 60% by weight, and preferably 85 to 65% by weight.
Although the manufacturing method of the propylene-ethylene block copolymer (B) used in the present invention has no particular restriction, it is preferably to apply to a similar method with the aforementioned method of the propylene-ethylene block copolymer (i) in the resin (A) except adjusting polymerization conditions to obtain the polypropylene-ethylene block copolymer (B). As the polymerization method, a batch-wise polymerization method is preferred from the viewpoint of less generation of granular structures.
The mixing ratios of the polypropylene resin (A) and the polypropylene resin (B) used in the present invention are from 95 to 80% by weight, preferably from 95 to 90% by weight, more preferably from 95 to 91% by weight, and 5 to 20% by weight, preferably from 5 to 10% by weight, more preferably from 5 to 9% by weight, respectively. Herein, the sum of the resins (A) and (B) is 100% by weight. When the mixing ratio of the polypropylene resin (A) exceeds 95% by weight, the die swell is reduced, so that the flow mark may become likely to occur, or the impact resistance of the molded product may be insufficient. Whereas, when it is less than 80% by weight, a large number of granular structures may occur, and the MFR of the polypropylene resin composition may be reduced, resulting in a reduction in flowability.
The polypropylene resin composition of the present invention comprises the polypropylene resin (A) and the propylene-ethylene block copolymer (B). The melt flow rate (MFR) thereof is from 5.0 to 150 g/10 min, and preferably from 10 to 120 g/10 min. When the melt flow rate (MFR) of the polypropylene resin composition of the present invention is from 5.0 to 150 g/10 min, a large molded article is easy to form. However, when it is less than 5.0 g/10 min, the moldability may be deteriorated, or flow marks may be generated. Whereas, when it exceeds 150 g/10 min, the impact resistance may be reduced.
The die swell of the polypropylene resin composition of the present invention is preferably not less than 1.6. When the die swell is less than 1.6, the flow marks of the molded article surface may unsatisfactorily increase.
As the manufacturing method of the polypropylene resin composition of the present invention, a method using a kneading machine such as a single screw extruder, twin screw extruder, Banbury mixer, hot roller or the like, is preferred. For example, methods shown below can be used.
(1) A method in which respective polymer powders of the polypropylene resin (A) and the propylene-ethylene block copolymer (B) are kneaded by using the aforesaid kneading machine.
(2) A method in which the polymer powder of the polypropylene resin (A) and the polymer powder of the propylene-ethylene block copolymer (B) are individually kneaded by using a single screw or twin screw extruder to prepare their respective pellets, and thereafter, the pellet of the polypropylene resin (A) and the pellet of the propylene-ethylene block copolymer (B) are kneaded by using a single screw or twin screw extruder.
(3) A method in which the propylene-ethylene block copolymer (B) previously pelletized by using a single screw or twin screw extruder is added to the kneading machine by using a constant amount feeder in the process of pelletizing the polymer powder of the polypropylene resin (A), and the mixture is kneaded.
Preferred is the method using the pellet of the propylene-ethylene block copolymer (B) previously kneaded by using a single screw or twin screw extruder of the aforesaid method (2) or (3).
Further, if required, a screen pack may also be mounted in a die of the single screw or twin screw extruder. As the screen pack to be mounted, preferred is a metal fiber sintered filter, which is, for example, described in xe2x80x9cMachine Design (1981, March issue, vol.25, No.3, 109-113)xe2x80x9d.
The kneading temperature is generally from 170 to 250xc2x0 C., and preferably from 190 to 230xc2x0 C.
Various additives may also be added to the polypropylene resin composition of the present invention as far as its purpose and effect are not damaged. Examples of the additives include antioxidants, UV absorbers, slipping agents, pigments, antistatic agents, copper harm inhibitors, flame retardants, neutralizing agents, foaming agents, plasticizers, nucleating agents, bubble inhibitors, and crosslinking agents. Among these additives, it is preferable that antioxidants and UV absorbers are added thereto for improving the heat resistance, weather resistance, and antioxidation stability. Further, the rubber components, various inorganic and organic fillers may also added thereto in such a range that the object and effect of the present invention are not damaged.
These additives, rubber components, fillers, and the like may be previously mixed with the polypropylene resin (A), the propylene-ethylene block copolymer (B), or both of them, and thereafter, the polypropylene resin composition is prepared. Alternatively, they may also be mixed therewith in the kneading stage of the polypropylene resin (A) and the propylene-ethylene block copolymer (B).
The polypropylene resin composition of the present invention can be molded into an injection-molded article by a generally known injection molding. Particularly, it is preferably used as an injection-molded article for an automobile, and preferably used as, for example, a door-trim, a pillar, an instrumental panel, a bumper, or the like.